This invention relates to anhydride-functional compositions of matter. In one embodiment, the invention relates to new anhydride curing agents for epoxy resins.
Standard monoanhydride curing agents for epoxy resins, such as phthalic anhydride, methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride, give resin/curing agent mixtures which are easily processed but cure to castings with low Tg values (usually below 200.degree. C.) when used with standard commercial difunctional liquid epoxy resins based on bisphenol A. Dianhydrides such as benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) give cured epoxy resins with high Tg values but short "processing windows" and liquid processing of such epoxy systems is difficult because of the high melting points of the anhydrides (225.degree. C. for BTDA and 286.degree. C. for PMDA, for example). The epoxy resin containing the powdered dianhydride has to be heated to very high temperatures in order to dissolve the powder, and in many cases it is difficult to dissolve the dianhydride completely before the system gels.
It is therefore an object of the invention to provide epoxy resin compositions which have good processing characteristics and high cured Tg.